| The new iron-based superconductor-LaO1-xFxFeAs found by Japanese researchers has induced an explosive research boom in the field of condensed matter physics since 2008. It is explored with high hopes to better explain the high-temperature superconducting mechanism perplexed academica all along. The new superconductors have some advantages over copper oxides. Such as longer coherence length, low anisotropy, inclining to machine processing and so on. In the branches of iron-based superconductors, FeSex binary compound is choosed to the main target of this study because of its simple structure, low toxicity, pressure sensitivity and doping characteristics.This paper focused on the faberication and properties measurement of the iron selenium bulks and selenized thin films. In the process of chemical synthesis of FeSe bulk superconductors, two methods (hydrothermal synthesis and organic synthesis) were compared in details. The optimal parameters were determined through the characterization of powders to obtain FeSex bulk with good performance in superconducting properties. For the preparation of FeSe superconducting thin films, the discrepancy of two selenizing ways (Fe and FeS precursor films) was analyzed. Specifically, both selenizing mechanisms (push filling and vacancy) were analyized thoroughly.The results include the following 3 points:(1) FeSe bulk prepared with the optimized organic synthesis after anealed in vaccum, pressed and sintered. Its superconducting properties were well displayed in ultra-low temperature transport measurement. Tc,onset= 11K, Tc,0=4 K. It was found that the appearance ofβnon-superconducting phase made resistivity decline moderatly;(2)The differences of selenizing Mechanisms of the two precursor films (Fe, FeS) were analyized with Atoms diffusion theory. The selenizing of Fe precursor films was in the interstitial "push filling" way. voids of a-Fe tetrahedral and octahedral were estimated much smaller than the atomic radius of selenium, which made severely lattice distortion by the squeezing of alien selenium atoms; the selenizing of FeS precursor films was in the Se-S atomic exchange way. The matrix of FeS was non-closepacked structure, so the whole selenizing reaction would not have a serious tensile stress;(3)The experimental results confirmed the above theory analysis. As a result of the release of lattice distortion, the surface of Fe appeared cracks and breakage to a certain extent after selenization. However, FeS film had holes slightly after selenizing treatment. FeSex films obtained by both methods had certain superconductivity. Tc, onset= 11 K, Tc,0=4.5 K. The transport results show considerable approximation with journals published in the condition of current pressure and undoped treatment. |
